The influence of superathermal electrons on the derivation of coronal electron temperatures from solar wind motor ion charge states

Abstract The CELIAS/CTOF (Charge Time Of Flight) mass spectrometer on board the SOHO mission measures the ionic and elemental composition of minor ions in the solar wind. From density ratios of adjacent charge states of minor ions we derive, consistent with previous measurements of the same type, mean freeze-in temperatures in the slow solar wind in the range between about 1.1 × 10 6 K and 1.6 × 10 6 K depending upon the charge states and elements considered. These values are obtained assuming a Maxwellian distribution of the electrons in the inner corona. We assess the influence of suprathermal electrons in the corona upon the density ratios and, subsequently, on the temperature estimates that are drawn from minor ion charge spectra. It was found that only limited amounts of suprathermal electrons are compatible with the charge state observations in the slow solar wind.